1. An accurate gene test can tell if a mutation is present, but that finding does not guarantee that disease will develop.

2. Because gene tests reveal information not only about the individual, but about his/her relatives and future offspring, the results can challenge family and other personal relationships. With whom should a person share test results? Do the other family members want to know?

3. Most diseases do not follow simple patterns of inheritance. Many factors influence a gene's ability to build proteins. For one thing, different mutations in the same gene can produce a wide range of effects. In cystic fibrosis, for example, the gene that controls mucus production can have more than 300 different mutations; some cause severe symptoms; some, mild symptoms; and some, no symptoms at all.